I would disagree. If a user has expanded the Table of Contents, they are focusing on that element of the UI. Having other elements in front of it would be annoying. This is also in keeping with how things work in the old webbook theme:

I would disagree. If a user has expanded the Table of Contents, they are focusing on that element of the UI. Having other elements in front of it would be annoying. This is also in keeping with how things work in the old webbook theme: